test: add smoke test for focus-event UI freeze regression

Verifies that window focus events don't block the main thread for >500ms,
covering both single focus and rapid 5x focus (Cmd+Tab spam) scenarios.
Completes the regression test requirement for the git-commands-off-main-thread fix.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/smoke/focus-no-freeze.spec.ts

@@ -0,0 +1,50 @@
+import { test, expect } from '@playwright/test'
+
+test.describe('Focus event does not freeze the UI', () => {
+  test.beforeEach(async ({ page }) => {
+    await page.goto('/')
+    await page.waitForLoadState('networkidle')
+  })
+
+  test('window focus event completes without blocking UI for >500ms', async ({ page }) => {
+    // Verify the app loaded
+    await expect(page.locator('[data-testid="sidebar"]').or(page.locator('nav')).first()).toBeVisible()
+
+    // Measure how long the UI is blocked after a focus event.
+    // We dispatch focus, then immediately schedule a rAF callback.
+    // If the main thread is blocked (sync IPC), the rAF callback is delayed.
+    const blockMs = await page.evaluate(() => {
+      return new Promise<number>((resolve) => {
+        const t0 = performance.now()
+        window.dispatchEvent(new Event('focus'))
+        requestAnimationFrame(() => {
+          resolve(performance.now() - t0)
+        })
+      })
+    })
+
+    // The focus handler must not block the main thread for more than 500ms.
+    // Before the fix, git_pull ran synchronously and blocked for 2-3 seconds.
+    expect(blockMs).toBeLessThan(500)
+  })
+
+  test('rapid focus events (5x) do not accumulate freezes', async ({ page }) => {
+    await expect(page.locator('[data-testid="sidebar"]').or(page.locator('nav')).first()).toBeVisible()
+
+    const totalMs = await page.evaluate(() => {
+      return new Promise<number>((resolve) => {
+        const t0 = performance.now()
+        for (let i = 0; i < 5; i++) {
+          window.dispatchEvent(new Event('focus'))
+        }
+        requestAnimationFrame(() => {
+          resolve(performance.now() - t0)
+        })
+      })
+    })
+
+    // 5 rapid focus events should still complete in under 500ms total
+    // thanks to the cooldown preventing redundant work.
+    expect(totalMs).toBeLessThan(500)
+  })
+})